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From: merlyn@iwarp.intel.com (Randal L. Schwartz)
Newsgroups: comp.lang.perl
Subject: Re: Binary fixed-length records
Message-ID: <1991Apr24.001205.10345@iwarp.intel.com>
Date: 24 Apr 91 00:12:05 GMT
References: <1991Apr23.202307.2454@kfw.COM>
Sender: news@iwarp.intel.com
Reply-To: merlyn@iwarp.intel.com (Randal L. Schwartz)
Organization: Stonehenge; netaccess via Intel, Beaverton, Oregon, USA
Lines: 53
In-Reply-To: dan@kfw.COM (Dan Mick)

In article <1991Apr23.202307.2454@kfw.COM>, dan@kfw (Dan Mick) writes:
| Often, I want to dump a file full of fixed-length records.  The one way I've
| been using is
| 
| #!/usr/local/bin/perl
| 
| $stbuf_def="ccCCCCCCSSII"; 		# unpack codes for struct
| $streclen=20;				# length of above in bytes
| $/ = 0777;				# slurp in the whole file
| $_ = <>;				# into $_
| 
| $inputlen = length($_);
| $offset = 0;
| 
| while ($inputlen > 0) {
| 	$rec = substr($_, $offset, $streclen);
| 
| 	<unpack and print $rec>
| 
| 	$inputlen -= $streclen;
| 	$offset += $streclen;
| }
| 
| 
| ...but it strikes me that 1) the "slurp in whole file" will fail someday,
| and 2) the copy in the substr() can't be efficient.
| 
| Anyone willing to take a crack?  (I'm aware that the surrounding goo
| might not be as efficient as possible; what I'm mostly worried about are
| the two points above).

Yeah, do something like:

$stbuf_def="ccCCCCCCSSII"; 		# unpack codes for struct
$streclen = length(pack($stbuf_def, ())); # length of above in bytes

while (read(STDIN, $buf, $streclen) == $streclen) {
	@fields = unpack($stbuf_def, $buf); # process $buf
}

This presumes that you don't *really* need the full power of the <>
construct... if you do, it'd be a bit trickier.

| If I could get the book, I would...

(What stops you? :-)

print pack("c*",unpack("c*","Just another Perl hacker,"))
-- 
/=Randal L. Schwartz, Stonehenge Consulting Services (503)777-0095 ==========\
| on contract to Intel's iWarp project, Beaverton, Oregon, USA, Sol III      |
| merlyn@iwarp.intel.com ...!any-MX-mailer-like-uunet!iwarp.intel.com!merlyn |
\=Cute Quote: "Intel: putting the 'backward' in 'backward compatible'..."====/